MSTP Aruba (multiple regions) and RSTP Meraki

[MartinL4]

Hi all,

Needing some thoughts on what to do over a specific issue between Meraki MS425 with RSTP enabled and a third-party owned Aruba switch running MSTP with mutliple regions. 

We replaced some catalyst switches which worked fine with the Aruba MSTP, but now switching to Meraki there is constant election process going on who should be root. The thought is to get the third-party switch to disable MSTP on the ports we connect to their switches on, therefore trunking our VLAN's to our meraki switches.

Thanks, 

[alemabrahao]

Well as far as I know it's not a good practice to use RSTP and MSTP mixed, or if you use one or the other.

[MartinL4]

Yes, unfortunately don't have any choice as the third-party support other clients with same switches. 

[Brash]

Are the Aruba switches running the standard MSTP or is it a vendor specific implementation?

If it's as per the standard I wouldn't expect constant elections unless the links between the switches keeps changing state. 

You could try increasing or lowering your switch priorities.

[MartinL4]

Tried this so far:

Meraki and Aruba downstream are competing for root

1. Tried lowering cost for Core switches - no change

2. Raised the cost for Core switches - no change - Downstream switch priority - 4096

Powered core 1 switch off to rule out switch stack issues - no change

- Disabled RSTP on port 12 on Core-02 facing Aruba downstream

- All traffic stopped flowing

- Disabled RSTP globally - no change

- Removed native vlan from port 12 - no change

- RSTP is back enabled globally and on port 12

Pings are successful when Aruba downstream is root

Once it changes to the Meraki device, pings drop

It does this in 20 second intervals, repeats

[Tore]

MSTP is in fact RSTP just with the possibility to create multiple instances.
Using default MSTP instance together with RSTP should work just fine.
Check if it is actually necessary to run multiple instance, or if one is enough.

[MartinL4]

Hi Tore, unfortunately they run MSTP with multiple instance as they support multiple customers. Including ourselves. Managed to get the core config from the HP side though.

stp instance 0 priority 4096
stp mode rstp
stp bpdu-protection
stp global enable

interface Bridge-Aggregation1
description to customer root switches
port link-type trunk
undo port trunk permit vlan 1
port trunk permit vlan xxxx
link-aggregation mode dynamic
stp root-protection

[Tore]

Ok, this configuration alone looks good for integrating with a Meraki Switch at least.

[MartinL4]

Hi Tore, you'd think so but there is root bridge elections constantly, even with the other core set to a lower priority.

[cmr]

Can you share your topology?  In my experience having 3rd party core with Meraki edge works fine, even with PVST or other multiple instance modes.  If Meraki is core then you need single instance MST on the 3rd party switches.  If you have 3rd party core, Meraki distribution and 3rd party edge then single MST is an absolute must, even then you might have odd issues...

[MartinL4]

I can share the basics:

User > Third-party owned Access > Aruba Core (with multiple MST instances) > LACP Trunk > Meraki Core 

[GIdenJoe]

The most important part is first to check where your root bridge lies.
Is the Aruba switching in the CORE/DISTRIBUTION and are they root also for the CIST?

Then you should not have any issues with a downstream Meraki that has regular priority values.

Or is it the other way around?  If so you'll have to draw out your MSTP topology and where the master port lives.

[PhilipDAth]

Is it a single link?  If so, ask them if they can filter the spanning tree packets so you don't see anything.

[MartinL4]

LACP on two connections